Growth rate and morphology of isotactic polystyrene crystals in solution at high supercoolings

Abstract

The morphology and temperature dependence of the lateral growth rate G are reported for isotactic polystyrene crystallized from 0.1% dimethyl phthalate solution at high supercoolings. The outline of a lamella is a rounded hexagon for the highest temperature and a ragged circle for lower temperatures. The edges of the lamellae become ragged and overgrowth is pronounced with decreasing temperature. A linear relationship is found between log( G η ) and 1 TΔT over a wide range of supercooling ( ΔT = T o d − T) from 70 to 170 K, where η is a retardation factor of Arrhenius form with an activation energy of 8400 K, and T o d is the equilibrium dissolution temperature. The value of T o d is determined to be 200°C by differential scanning calorimetry. In these high supercoolings, the nucleation theory of polymer crystallization loses its validity; in fact, the slope of the plot of log( G η ) versus 1 TΔT is four times as large as the value predicted by nucleation theory. Possible growth mechanisms at high supercoolings are discussed on the basis of the morphology.